The present invention relates generally to crystal oscillator circuits and, more particularly, relates to a crystal oscillator circuit employing a power saving sleep mode.
Crystal oscillator circuits have many applications, one of the most common being to provide a clock signal required by a digital system. Most systems have required electrical characteristics for the clock signal such as the voltage swing, typically from 0 to 5 volts, and the output current drive.
The crystal oscillator circuit consumes a substantial amount of current, typically on the order of milliamps, to achieve the required characteristics. For systems utilizing a battery as a power supply the current consumed by the crystal oscillator circuit is a substantial load on the battery and reduces battery life.
Accordingly, many battery-powered portable systems, such as laptop computers, turn off the crystal oscillator circuit when the clock signal is not required. However, when the crystal oscillator is turned back there is a delay, typically on the order of milliseconds, before the output signal is stable and exhibits the required electrical characteristics. In certain applications, this delay is undesirable and adversely affects the operation of the system.